Kiyoshi Nagai FRS (June 25, 1949 – September 27, 2019) was a Japanese structural biologist at the MRC Laboratory of Molecular Biology Cambridge, UK.

Nagai studied at Osaka University and earned a Doctor of Philosophy under the supervision of Hideki Morimoto working on the allosteric effect in hemoglobin.

[1] In 1981 Nagai moved to the MRC Laboratory of Molecular Biology where he worked as a post-doc with Max Perutz on overproduction of eukaryotic proteins in E.

[2][3] In 1987 he became a tenured group leader at the LMB and was joint head of the Division of Structural Studies from 2000 to 2010.

[13][14] Nagai's subsequent structures of spliceosomes in various stages of assembly and catalysis[15][16] combined with structures from the groups of Reinhard Lührmann, Yigong Shi and others have provided crucial insight into the catalytic mechanism of pre-mRNA splicing.